1. Field of the Invention
The invention relates generally to locking systems and more particularly to a remotely controlled system for locking a door.
2. Description of the Prior Art
Various systems for remotely controlling door locks have been described in the prior art. Both pneumatically and electrically controlled systems have been provided to permit doors to be remotely locked and unlocked. Pneumatically controlled systems typically include a pneumatically operated locking bolt which extends and retracts between the door to be locked and the frame in which the door is mounted. These systems normally utilize a pneumatically controlled plunger which is directly connected to the locking bolt so that displacement of the plunger results in a corresponding displacement of the locking bolt into or out of engagement with the door or the door frame. Such systems are disclosed in the following patents: U.S. Pat. Nos. 3,926,460; 1,154,439; 913,700; and British Patent No. 750,705. Another type of pneumatically controlled locking system is described in U.S. Pat. No. 3,624,761 which includes a pneumatically operable plunger engaging a locking pin received by the lock when the door is in a closed position. Another pneumatically controlled locking system is disclosed in my U.S. Pat. No. 4,005,885.
While the above patents all provide means for remotely controlling a door or window lock, these structures are not suitable for use as a part of a lock which is integral with a rotatable door handle.
A remotely actuated, electrically controlled locking system is disclosed in U.S. Pat. No. 4,073,527 to Schlage. This patent describes a door lock having a solenoid which, when used with conventional switches, displaces various components within an integral door handle lock to permit the lock to be controlled from a remote position. This system is therefore adapted for use in a commercial or industrial building where a single station controls the locked or unlocked mode of a plurality of locks, or in an apartment-type building where a plurality of stations control the mode of a single entry lock. The Schlage patent describes a door lock having a solenoid which selectively reciprocates along an axis which is perpendicular to the axis of rotation of the door handles. An alternate embodiment includes a simple thumb turn with a solenoid adapted to selectively reciprocate along the axis of rotation of the thumb turn.
More pertinent to the present invention are the commercial designs of the Schlage Lock Company, the assignee of the Schlage patent. One such locking system, designated model No. D80PDEL, is an electrically controlled lock which includes an electrical solenoid which is selectively reciprocated along the axis of rotation of the door handles. Reciprocation of the solenoid results in displacement of locking portions of the door lock to permit the lock to be remotely controlled. This model is electrically locked by continuous current until unlocked by operation of a switch, power failure, or through the use of a key. Schlage model No. D80PDEU is similar to the aforedescribed model except that it is mechanically held in a locked mode until mechanically unlocked by a key or electrically unlocked by electric current. Primarily because of the heat which builds up during operation, this system is specifically designed only for intermittent operation.
The Schlage locks thus provide a means for modifying conventional door handle locks for remote control. However, there are a number of drawbacks inherent with this type of electrical control system. With respect to model No. D80PDEL, which is electrically locked, power failure will necessarily result in all of the electrically controlled doors being unlocked. Thus, to obtain unauthorized entrance, one need only shut down the electrical system. Inadvertent opening of a particular lock may also occur in the event of a slight short in the lock circuitry. Moreover, since electricity is drawn by the locking system at all times the system is in locked mode, the operating cost could be substantial. It might also provide a fire hazard which could be particularly acute when the system is mounted within a wooden door, which is very often the case. With model No. D80PDEU, which is electrically unlocked, the locks may only be operated a certain number of times within a given time period because nothing is provided for dissipating the heat generated within the solenoid during repeated actuation. Also, in the event of a loss of power, no means is provided for unlocking the system without the use of a key; that is, there is no override capability other than the use of a key which could prove inconvenient and perhaps even dangerous during an emergency.
The described electrical locking systems also exhibit an inferior alarm sensing capability. Thus, for example, in the event of loss of power to a particular lock, no one would necessarily know without actually testing the lock that it was not operating in a perfectly normal manner. The use of an electrical solenoid renders it extremely difficult and therefore expensive to position insulated microswitches which sense the position of the solenoid and which could be mounted into the door to serve as an alarm. In the event such sensing capability would be built externally of the lock but within the door, installation of the lock would be far more difficult than with conventional locks.
Hence it is a primary object of the present invention to provide an improved remotely controlled locking system which effectively and reliably overcomes the aforementioned limitations and drawbacks of the prior art proposals. More specifically, the present invention has as its objects one or more of the following taken individually or in combination:
(1) The development of a remotely controllable locking system which in external appearance is no different from a conventional, nonremotely controlled door lock;
(2) The provision of a remotely controllable locking system which is fail-safe in that in the event of total loss of the control medium, the lock will remain in a locked position, thereby reducing the possibility of unauthorized entry;
(3) To develop a remote controlled locking system which can have a sensing capability built into it to sense when there is a loss of control function;
(4) The development of a remote controlled locking system which is operable at a minimal of expense and does not increase fire hazards; and
(5) To provide a remote control locking system which is simple in construction, yet which provides means for positively locking and unlocking a large number of doors from one or more remote locations.